1. Field of the Invention
The present invention relates in general to certain new and useful improvements in methods for producing reinforced plastic sheets and reinforced plastic laminated structures, and more particularly, to methods for producing reinforced plastic sheets and laminated structures having fiber reinforced plastic components included therein, and which relies upon moving belts engaging the components and air or other gas under pressure creating a pocket to support the belts to facilitate the laminating process or the curing process.
2. Brief Description of the Prior Art
In recent years, reinforced plastics have achieved increasing prominence and have found applications in many areas which were previously satisfied by products fabricated of heavy metal and other structural materials. Furthermore, improved raw material prices and increased availability of reinforced plastic materials has favored the use of reinforced plastic materials in the production of rigid flat sheets and plastic sheet laminates and structural members. It is well known in the reinforced plastic composites industry that flat fiberglass reinforced plastic panels can be produced by curing a resin matrix impregnated into fiber-containing reinforcing material. Flat reinforced plastic panels can be produced by a laminable procedure in which one or a plurality of the resin impregnated fiberglass sheets are laminated in juxtaposition, and then cured in a large oven or curing device.
These reinforced plastic sheets and the laminate structures which include at least one reinforced plastic composite layer as well as a rigid panel laminated to each other are often referred to as reinforced plastic flat sheet structures or reinforced plastic flat sheet laminate structures. One such device for producing these structures is more fully illustrated and described in U.S. Pat. No. 3,801,407, dated Apr. 2, 1974, to Goldsworthy et al. In this, as well as other apparatus method for producing reinforced composite flat sheet structues, at least one or more fiber-reinforced resin-impregnated layers is brought into facewise contact with a relatively rigid panel, as for example, a plywood or similar panel. These laminable layers are then compressed between one or more pairs of opposed rollers. These rollers serve as the primary force to urge the laminated members into intimate contact with one another. Thereafter, the reinforced plastic layer is subjected to a curing environment in which the resin matrix, which is impregnated in the fibers contained in the fiber-containing reinforced plastic layer, are cured and which simultaneously bond to the rigid panel, such as a plywood sheet.
It has been found that reinforced plastic sheet structures of this type can find a wide variety of uses as substitutes for considerably more expensive rigid sheet structures. These reinforced sheet structures can find use in many forms of industries, particularly in the construction of buildings, as for example, side walls of houses and the like. These structures can be used in building bulkheads in ships, in the fabrication of trailer bodies and intermodal containers, and in like stuctures. Moreover, and of significant importance, is the fact that reinforced laminate sheet structures of this type can be produced by using relatively low grades of rigid panels. Consequently, it is possible to produce very low-cost rigid structures by the apparatus and method of the present invention.
One of the principal problems in creating these flat sheet laminate structures is that it is necessary to obtain even contact with generally uniform pressure of the reinforced plastic composite layer on the rigid panel across the bonding surface thereof, or otherwise a lack of uniform bonding will result. Previously, the prior art techniques for producing such structures employed various means of bringing the one or more reinforced plastic sheets into contact with the rigid panel, as for example, by the use of roller bearings or flat platens which force the juxtaposed laminable members into contact with each other. However, these prior art techniques did not resolve the problem of uneven bonding which resulted in structurally and aesthetically inferior products.
A similar problem arises in the production of reinforced plastic sheets which are not laminated to a rigid panel. In this case, the resin impregnated in one or more layers of fiber-containing material, such as roving strands, tapes or woven or nonwoven sheet material is cured to form a rigid sheet. However, it is necessary to employ substantial and continuous and even pressure across the sheet of material during the curing process to provide a sheet with the desired strength and physical properties. The apparatus of the prior art were also not effective for this purpose since they did not offer a mechanism to apply the continuous and even pressure during the laminating process. Further, the prior art devices were capable of applying pressure to limited transverse cross section areas and were not adapted to apply uniform pressure across the transverse dimension and a substantial segment lengthwise of the laminable members.
One of the other problems encountered in the prior art techniques of producing reinforced plastic flat sheet structures was the fact that excess heat was applied to the one or more layers or members of the laminate structure during the production thereof which resulted in boiling of the resin matrix around the edges of the sheets. Consequently, in many of the prior art attempts to produce the reinforced plastic structures, volatilization of the resin matrix occurred which resulted in the premature curing of the flat sheet structure with the resultant significant reduction in inherent strength in the final product, as well as the aesthetic appearance thereof.
U.S. Pat. No. 3,674,601, dated July 4, 1972, teaches of an augmented curing system for pultruded reinforced plastic stocks. In this apparatus, a cure of the thermosetting resin impregnated in the fiber containing strands is initiated in an initial curing stage. Before final curing the stock is pulled through a die which is externally heated so that the stock is cured to completion. However, this augmented curing mechanism was not effectively used in producing flat sheet materials.
The present invention obviates these and other problems in providing an apparatus and method which provides uniform contact and relatively uniform pressure to the surfaces of the laminable members during the manufacture thereof, also avoids any excessive heat generation which results in the volatilization of the resin matrix, and/or steaming of moisture in the core material and a means and method for creating a void filling surface film.